This invention relates generally to microphones and particularly to boundary layer or pressure zone microphones.
A boundary layer or pressure zone microphone is a microphone which is situated proximate to a boundary layer or pressure zone created by a reflecting surface. Sound waves create a high pressure region directly in front of a sound reflecting surface. The incident and reflected waves from a reflecting surface are superimposed in the same phase. Thus, the pressure in front of the surface may be twice as high as in the free sound field. This effect is utilized in so-called boundary layer or pressure zone microphones. In one embodiment of such microphones, an electrical transducer is mounted on a flat, reflecting surface. The increased acoustic pressure is then detected by the microphone in the region proximate to the reflecting surface.
The pressure zone or zone of increased pressure is at a maximum at a distance of half the sound wavelength from the reflecting surface. Thus, microphones built into the reflecting surface may have a sensitivity that is twice the value that the microphone would have without the,reflecting surface.
Conventional microphones may also be used with sound reflectors which concentrate the sound at the transducer. For example, a parabolic reflector may be utilized with a rearwardly facing transducer located at the focal point of the parabolic reflector. The transducer then receives the concentrated sound waves from the reflector and converts them into an electrical signal. One problem with this approach is that such microphones are particularly prone to feedback effects.
Thus, there is a need for improved microphones that take advantage of the acoustic gain achievable using a boundary layer or pressure zone.
In accordance with one aspect, a microphone may include a concave reflector. A boundary layer creating surface is opposed to the concave reflector.
Other aspects are set forth in the accompanying detailed description and claims.